1. Field of the Invention
The invention relates generally to a process for converting a particulate solid biomass material to a high quality bio-oil in high yield, and more particularly to a pretreatment process in which the solid biomass material is at least partially demineralized and whereby the accessibility of the biomass material is enhanced.
2. Description of the Related Art
Processes for converting biomass material to liquid reaction products are known. Flash pyrolysis is generally recognized as providing a high yield of liquid pyrolysis products.
The quality of product obtained with flash pyrolysis tends to be poor, as evidenced by the high oxygen content and the high total acid number of such products. As a result of the high oxygen content, the pyrolysis oil does not spontaneously separate into an aqueous phase and an oil phase. Moreover, due to the high acid content, the products are highly corrosive and require to be stored and treated in equipment made of special alloys.
It is generally recognized that minerals present in solid biomass materials affect the product yields of pyrolysis conversion reactions. It has been shown in academic papers that removal of minerals from solid biomass materials results in a higher liquid yield at the expense of the coke yield and the gas yield.
Processes used in the literature to remove minerals from solid biomass are not suitable for operation on an economic scale. For example, HCl and sulfuric acid have been proposed as solvents for extracting minerals from biomass materials. Use of these mineral acids makes the process expensive and requires cumbersome recovery processes. Moreover, the use of strong acids results in hydrolysis of hemicellulose, and hence a loss of valuable carbon from the feedstock.
Sodium hydroxide has been proposed as well. Alkaline solutions however are known to solubilize lignin. Indeed, alkaline solutions are used in the Kraft process for removing lignin from papermaking cellulose fibers. Therefore, the use of sodium hydroxide also results in a significant loss of valuable carbon from the feedstock.
Thus, there is a particular need for a process for the mineralization of solid biomass material that utilizes readily available low-cost solvents and does not result in an unnecessary loss of carbon from the biomass feedstock.